Power supply control device and image forming apparatus

ABSTRACT

A power supply control device includes a switch to output a switch depression signal, which is in a first logic level during a period in which the switch is not depressed, and is in a second logic level during a period in which the switch is depressed, a first power supply to generate a first DC voltage based on AC power, which is supplied from an outside, and to apply the first DC voltage to a predetermined load, and a second power supply configured to generate a second DC voltage based on the AC power irrespective of a state of the switch, and a controller to operate on the second DC voltage, to switch an operation state of the first power supply when the switch depression signal has switched from a first logic level to a second logic level and remains at the second logic level.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a power supply control technology forapparatus, such as an image forming apparatus.

Description of the Related Art

Apparatus, such as an image forming apparatus, each include a main powerswitch for starting (turning on) and shutting down (turning off) a mainbody thereof. The apparatus is started or shut down when the main powerswitch is operated under a state in which a commercial power supply andthe apparatus are connected to each other. The apparatus starts powersupply from an internal power supply, which is included in the mainbody, to components in the main body to enter an operable state whenbeing started. The apparatus stops power supply from the internal powersupply to the components in the main body when being shut down. As themain power switch, a push switch in which a contact is connected onlywhen the push switch is operated can be used, for example.

The apparatus is controlled by firmware or software so as to be startedthrough an operation on the push switch when the apparatus is in ashutdown state, and to be shut down through an operation on the pushswitch when the apparatus is in the operable state. The firmware orsoftware is executed by a central processing unit (CPU) to control startand shutdown of the apparatus. The firmware or software cannot normallycontrol start and shutdown of the apparatus anymore when the CPU getsout of control. In this case, an operation on the main power switch whenthe apparatus is in the operable state cannot stop the apparatus, forexample.

In Japanese Patent Application Laid-open No. 2003-15780, there isdisclosed a power supply control device capable of addressing theabove-mentioned situation and shutting down the apparatus reliably. Thispower supply control device forcefully stops power supply from theinternal power supply to the components when a signal for giving aninstruction to stop power supply is not transmitted from the firmware tothe internal power supply after a predetermined time period has elapsedsince an operation on a main power switch. In this manner, the apparatusis shut down even when the CPU gets out of control.

However, when the main power switch using the push switch itself failsdue to an abnormality, the instruction to stop power supply is nottransmitted from the main power switch to the CPU anymore. In this case,a situation in which the apparatus is not shut down even when the CPU isin normal operation occurs. In view of the above-mentioned problem, thepresent disclosure has a main objective to provide a power supplycontrol device capable of detecting a failure of a main power switch.

SUMMARY OF THE INVENTION

A power supply control device of the present disclosure includes: aswitch configured to output a switch depression signal, which is in afirst logic level during a period in which the switch is not depressed,and is in a second logic level during a period in which the switch isdepressed; a first power supply configured to generate a first DCvoltage based on AC power, which is supplied from an outside, and toapply the first DC voltage to a predetermined load; a second powersupply configured to generate a second DC voltage based on the AC powerirrespective of a state of the switch; and a controller configured tooperate on the second DC voltage, to switch an operation state of thefirst power supply in a case where the switch depression signal hasswitched from the first logic level to the second logic level andthereafter the switch depression signal remains at the second logiclevel until a first predetermined time period has elapsed, and to outputa signal on a failure of the switch in a case where the switchdepression signal has switched from the first logic level to the secondlogic level and thereafter the switch depression signal remains at thesecond logic level until a second predetermined time period has elapsed,the second predetermined time period being longer than the firstpredetermined time period.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an appearance view of an image forming apparatus.

FIG. 2 is an explanatory diagram of a power supply control device.

FIG. 3A, FIG. 3B, and FIG. 3C are flow charts for illustratingprocessing to be performed when the image forming apparatus is started.

FIG. 4A, FIG. 4B, and FIG. 4C are flow charts for illustratingprocessing to be performed when the image forming apparatus is shutdown.

FIG. 5A and FIG. 5B are timing charts obtained when the image formingapparatus is started.

FIG. 6A and FIG. 6B are timing charts obtained when the image formingapparatus is stopped.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention is described with reference tothe drawings.

FIG. 1 is an appearance view of an image forming apparatus employing apower supply control device according to an embodiment of the presentdisclosure. An image forming apparatus 100 includes a power supplyportion 104 configured to supply external AC power from a commercialpower supply through an outlet, a main power switch 103, an operationpanel 102, and a display 101. The operation panel 102 is an inputdevice, through which a user inputs an instruction to the image formingapparatus 100. The display 101 is an output device, on which anoperation status, an operating condition, and various messages of theimage forming apparatus 100 are displayed. The image forming apparatus100 is switched in operation state through an operation on the mainpower switch 103. Through an operation on the main power switch 103, theoperation state is switched to an operable state upon startup from ashutdown state, or from the operable state to the shutdown state. Theimage forming apparatus 100 is configured to form an image on a givensheet in response to an instruction from the user.

FIG. 2 is an explanatory diagram of the power supply control deviceconfigured to control a power supply system of the image formingapparatus 100. The power supply control device includes a CPU 202, afirst power supply 207, a second power supply 208, a DC/DC converter210, and a power transistor 211. The CPU 202 is a controller configuredto execute a predetermined computer program to function as a depressiontime period counter 203, an error determination unit 204, and a powersupply controller 205. The CPU 202 is configured to control operation ofthe image forming apparatus 100. In this specification, a function ofcontrolling the power supply system by the CPU 202 is described, and adescription on other functions is omitted.

To the first power supply 207 and the second power supply 208, theexternal AC power is supplied from the commercial power supply. Thefirst power supply 207 is controlled in operation by the CPU 202, and isconfigured to supply power to a load 209, for example, a motor to beused in forming an image. The first power supply 207 in this embodimentis configured to convert the external AC power to generate a DC voltageof 24 V for use inside the apparatus, and to apply the DC voltage to theload 209. The first power supply 207 is configured to start the imageforming apparatus 100 in response to an instruction from the CPU 202based on an operation on the main power switch 103.

The second power supply 208 is configured to operate irrespective of theoperation on the main power switch 103, and to supply power to the DC/DC210. The second power supply 208 in this embodiment is configured toconvert the external AC power into a DC voltage of 12 V for use insidethe apparatus, and to apply the DC voltage to the DC/DC converter 210.The DC/DC converter 210 is configured to convert the DC voltage of 12 Vapplied from the second power supply 208 into a DC voltage of 3.3 V, andto supply the DC voltage to the main power switch 103 and the CPU 202.Further, the second power supply 208 can apply the DC voltage of 12 V tothe display 101 via the power transistor 211. The power transistor 211is an energization controller provided on a path through which the DCvoltage is supplied from the second power supply 208 to the display 101to control energization of the display 101 with the DC voltage.

The main power switch 103 is formed of a push switch, and a switchdepression signal 212 has a low logic level under a state in which themain power switch 103 is not depressed. The switch depression signal 212is switched to a high logic level during a period in which the mainpower switch 103 is depressed. In this embodiment, the DC voltage of 3.3V is supplied from the DC/DC converter 210 to the main power switch 103.Therefore, during the period in which the main power switch 103 isdepressed and conductive, the switch depression signal 212 is at 3.3 V(high logic level). A signal line between the main power switch 103 andthe CPU 202 is grounded via a resistor, and hence the switch depressionsignal 212 is at 0 V (low logic level) during a period in which the mainpower switch 103 is not depressed.

The CPU 202 is active at all times with the DC voltage of 3.3 V appliedfrom the DC/DC converter 210 irrespective of an operation on the mainpower switch 103. The CPU 202 is configured to switch the operationstate of the image forming apparatus 100 with the switch depressionsignal 212 acquired from the main power switch 103.

(Operation Upon Normal Startup)

Upon startup of the image forming apparatus 100, the power supplycontrol device operates as follows. This operation is started withdepression of the main power switch 103 for startup when the imageforming apparatus 100 is in the shutdown state, in which no power issupplied to components of the image forming apparatus 100. In a casewhere the main power switch 103 is depressed, the switch depressionsignal 212 at the high level is input from the main power switch 103 tothe CPU 202. The switch depression signal 212 is input to the depressiontime period counter 203 of the CPU 202. The depression time periodcounter 203 is configured to count a time period during which the switchdepression signal 212 is continuously at the high level. A counted timeperiod 213 obtained by the depression time period counter 203 is inputto the error determination unit 204. The depression time period counter203 is configured to continuously perform the counting during a periodin which the switch depression signal 212 is at the high level, and totransmit the latest counted time period 213 to the error determinationunit 204 during the period.

The error determination unit 204 is configured to compare the countedtime period 213 with a predetermined time period (a time period Ton/off(for example, 50 milliseconds)), and to determine whether or not toperform startup processing based on a result of the comparison. Forexample, the error determination unit 204 performs the startupprocessing in a case where the counted time period 213 is the timeperiod Ton/off or more, and transmits a power supply control instructionsignal 214 for activating the first power supply 207 to the power supplycontroller 205. In a case where the counted time period 213 is less thanthe time period Ton/off, the startup processing is not performed.

The power supply controller 205 is configured to enable a first powersupply ON signal 217 for activating the first power supply 207 inresponse to the power supply control instruction signal 214 foractivating the first power supply 207. With the first power supply ONsignal 217 being enabled, the first power supply 207 applies the DCvoltage of 24 V to the load 209. The power supply controller 205 alsoenables a power transistor ON signal 216 (changes the power transistorON signal 216 to a high level) in order to put the power transistor 211into a conductive state. The power transistor 211 becomes conductive ina case where the power transistor ON signal 216 is enabled. When thepower transistor 211 becomes conductive, the path through which the DCvoltage is supplied from the second power supply 208 to the display 101passes an electric current to apply the DC voltage of 12 V to thedisplay 101.

In a case where the DC voltage is applied to the load 209 and thedisplay 101 and no other error has occurred, the image forming apparatus100 performs an initial operation and enters a standby state (operablestate) in which various jobs can be received. This completes processingof supplying power to the components by the power supply control deviceupon startup of the image forming apparatus 100.

(Operation Upon Normal Shutdown)

Upon shutdown of the image forming apparatus 100, the power supplycontrol device operates as follows. This operation is started withdepression of the main power switch 103 for shutdown in a case where theimage forming apparatus 100 is in the operable state, in which power issupplied to the components of the image forming apparatus 100. In a casewhere the main power switch 103 is depressed, the switch depressionsignal 212 at the high level is input from the main power switch 103 tothe CPU 202. The switch depression signal 212 is input to the depressiontime period counter 203 of the CPU 202. As in the startup, thedepression time period counter 203 is configured to count a time periodduring which the switch depression signal 212 is continuously at thehigh level. The counted time period 213 obtained by the depression timeperiod counter 203 is input to the error determination unit 204. Thedepression time period counter 203 is configured to continuously performthe counting during a period in which the switch depression signal 212is at the high level, and to transmit the latest counted time period 213to the error determination unit 204 during the period.

As in the startup, the error determination unit 204 is configured tocompare the counted time period 213 with the time period Ton/off, and todetermine whether or not to perform shutdown processing based on aresult of the comparison. For example, in a case where the counted timeperiod 213 is the time period Ton/off or more, the error determinationunit 204 performs the shutdown processing and transmits the power supplycontrol instruction signal 214 for deactivating the first power supply207 to the power supply controller 205. In a case where the counted timeperiod 213 is less than the time period Ton/off, the shutdown processingis not performed.

The power supply controller 205 dissembles the first power supply ONsignal 217 (changes the first power supply ON signal 217 to a low level)in response to the power supply control instruction signal 214 fordeactivating the first power supply 207. The first power supply 207stops applying the DC voltage to the load 209 when the first powersupply ON signal 217 becomes the low level. The power supply controller205 also changes the power transistor ON signal 216 to a low level inorder to cut off (turned off) the power transistor 211. The powertransistor 211 is cut off when the power transistor ON signal 216becomes the low level. When the power transistor 211 is cut off, theapplication of the DC voltage from the second power supply 208 to thedisplay 101 is stopped. This completes processing of stopping powersupply to the components by the power supply control device uponshutdown of the image forming apparatus 100. In the processing ofstopping power supply, the second power supply 208 is not deactivated,and the DC voltage of 3.3 V remains being applied to the CPU 202.Therefore, the CPU 202 is active even after the processing of stopping.

(Operation Upon Startup During the Main Power Switch 103 has Failed)

In a case where the main power switch 103 has failed upon startup of theimage forming apparatus 100, the power supply control device operates asfollows. In a case where the main power switch 103 fails, the logiclevel of the switch depression signal 212 does not change anymore. Inother words, the switch depression signal 212 becomes a signal having alogic level that is always high or low. In a case where the switchdepression signal 212 is low, the image forming apparatus 100 is notstarted. In a case where the switch depression signal 212 is high, thefollowing operation is performed.

Processing of from the first power supply 207 applying the DC voltage of24 V to the load 209 to the second power supply 208 applying the DCvoltage of 12 V to the display 101 is the same as in the case of normalstartup. However, the switch depression signal 212 is continuously inthe high state. Therefore, the depression time period counter 203continues counting. The error determination unit 204 compares thecounted time period 213 with a predetermined time period (time periodTen (for example, 5 seconds)). The time period Ten is longer than thetime period Ton/off. While the counted time period 213 is less than thetime period Terr, the error determination unit 204 continues to transmitthe power supply control instruction signal 214 for activating the firstpower supply 207 to the power supply controller 205.

In a case where the counted time period 213 reaches the time periodTerr, there is a fear that the main power switch 103 has failed and acontact remains connected. In other words, the switch depression signal212 is always high. In this case, even when the main power switch 103 isdepressed in order to shut down the image forming apparatus 100, theswitch depression signal 212 does not change. Therefore, the powersupply to the image forming apparatus 100 cannot be stopped. Further, itis uncertain from the outside whether the power supply to the imageforming apparatus 100 cannot be stopped due to a failure of the mainpower switch 103, or the power supply cannot be stopped for otherreasons.

In order to resolve the situation in which the power supply cannot bestopped, the error determination unit 204 transmits the power supplycontrol instruction signal 214 for forcefully deactivating the firstpower supply 207 to the power supply controller 205 in a case where thecounted time period 213 reaches the time period Terr. The power supplycontroller 205 changes the first power supply ON signal 217 to the lowlevel in response to the power supply control instruction signal 214 forforcefully deactivating the first power supply 207. In a case where thefirst power supply ON signal 217 becomes the low level, the first powersupply 207 stops applying the DC voltage to the load 209.

The power transistor 211 is maintained in the conductive state, and thedisplay 101 is active. The error determination unit 204 transmits adisplay instruction signal 215 indicating that the main power switch 103has failed to the display 101. Thus, a message which indicates that themain power switch 103 has failed is displayed on the display 101, forexample.

(Operation Upon Shutdown During the Main Power Switch 103 has Failed)

In a case where the main power switch 103 has failed upon shutdown ofthe image forming apparatus 100, the power supply control deviceoperates as follows.

Processing up to the first power supply 207 stopping application of theDC voltage to the load 209 is the same as in the case of normalshutdown. It should be noted, however, that the power transistor 211 ismaintained in the conductive state, and the display 101 is active. Theswitch depression signal 212 is continuously in the high state.Therefore, the depression time period counter 203 continues counting.The error determination unit 204 compares the counted time period 213with the time period Ten. While the counted time period 213 is less thanthe time period Terr, the error determination unit 204 continues totransmit the power supply control instruction signal 214 fordeactivating the first power supply 207 to the power supply controller205.

In a case where the counted time period 213 reaches the time periodTerr, there is a fear that the main power switch 103 has failed and thecontact is always connected. In other words, the switch depressionsignal 212 is always high. In this case, even when the main power switch103 is depressed in order to start the image forming apparatus 100 thathas been shut down, the switch depression signal 212 does not change.Therefore, the power supply to the image forming apparatus 100 cannot bestarted. Further, it is uncertain from the outside whether the powersupply to the image forming apparatus 100 cannot be started due to afailure of the main power switch 103, or the power supply cannot bestarted for other reasons.

In order to resolve the situation in which the power supply cannot bestarted, the error determination unit 204 transmits the displayinstruction signal 215 indicating that the main power switch 103 hasfailed to the display 101 in a case where the counted time period 213reaches the time period Terr. Thus, a message which indicates that themain power switch 103 has failed is displayed on the display 101, forexample.

(Processing Upon Startup)

FIG. 3A to FIG. 3C are flow charts for illustrating processing uponstartup of the image forming apparatus 100.

The CPU 202 determines whether the main power switch 103 has beendepressed and the switch depression signal 212 has changed from low tohigh (Step S301). In a case where the switch depression signal 212 haschanged from low to high (Step S301: Y), the CPU 202 performs activationdetermination processing for the first power supply 207 (Step S302). Inthe activation determination processing for the first power supply 207,it is determined whether the main power switch 103 has been depressedfor the predetermined time period (time period Ton/off) or more. Withthis processing, it is possible to prevent such an erroneous operationas in a case where the user has erroneously depressed the main powerswitch 103, for example.

In FIG. 3B, the activation determination processing for the first powersupply 207 in Step S302 is illustrated. The CPU 202 starts counting thetime period during which the switch depression signal 212, which isacquired from the main power switch 103, is at the high level by thedepression time period counter 203 (Step S305). The error determinationunit 204 determines whether the counted time period 213 obtained by thedepression time period counter 203 has reached the time period Ton/offor more (Step S306).

In a case where the counted time period 213 has not reached the timeperiod Ton/off (Step S306: N), the CPU 202 determines whether the switchdepression signal 212 has changed to the low level (Step S307). In acase where the switch depression signal 212 remains at the high level(Step S307: N), the CPU 202 compares the counted time period 213 and thetime period Ton/off again by the error determination unit 204.

In a case where the switch depression signal 212 has changed to the lowlevel (Step S307: Y), the CPU 202 determines that the depressed state ofthe main power switch 103 has been canceled before the startupprocessing is started. In this case, the CPU 202 clears the counted timeperiod 213 of the depression time period counter 203 to 0, and endscounting the time period by the depression time period counter 203 (StepS308 and Step S309). The CPU 202 returns to the processing of Step S301without performing the startup processing. This is processing performedin the case of an erroneous operation by the user.

In a case where the counted time period 213 has reached the time periodTon/off (Step S306: Y), the CPU 202 ends the activation determinationprocessing for the first power supply 207. This is processing performedin a case of an instruction to start intended by the user.

In a case where the main power switch 103 is continuously depressed forthe predetermined time period or more and the activation determinationprocessing for the first power supply 207 is ended, the CPU 202activates the first power supply 207 and the display 101 (Step S303).The CPU 202 enables the first power supply ON signal 217 by the powersupply controller 205. In a case where the first power supply ON signal217 is enabled, the first power supply 207 is activated to apply the DCvoltage to the load 209. The CPU 202 also enables the power transistorON signal 216 (changes the power transistor ON signal 216 to the highlevel) in order to put the power transistor 211 into the conductivestate. In a case where the power transistor 211 becomes conductive, thepath through which the DC voltage is supplied from the second powersupply 208 to the display 101 passes an electric current to apply the DCvoltage to the display 101. In a case where the DC voltage is applied,the display 101 is activated.

Next, the CPU 202 performs failure determination processing for the mainpower switch 103 (Step S304). In FIG. 3C, the failure determinationprocessing for the main power switch 103 in Step S304 is illustrated.

The CPU 202 determines whether the counted time period 213, whichindicates the time period during which the switch depression signal 212is at the high level, has reached the time period Terr or more (StepS311). In a case where the counted time period 213 is less than the timeperiod Ten (Step S311: N), the CPU 202 determines whether the switchdepression signal 212 has changed to the low level (Step S315). In acase where the switch depression signal 212 remains at the high level(Step S315: N), the CPU 202 compares the counted time period 213 and thetime period Terr again by the error determination unit 204.

The switch depression signal 212 having changed to the low level (StepS315: Y) means that the depressed state of the main power switch 103 hasbeen canceled after the startup processing. In this case, the CPU 202clears the counted time period 213 of the depression time period counter203 to 0, and ends counting the time period by the depression timeperiod counter 203 (Step S316 and Step S317). This is processingperformed in the case of normal operation. In the case of normaloperation, the switch depression signal 212 changes to the low levelafter the state of high level has continued for the time period Ton/offor more, and for less than the time period Ten.

In a case where the counted time period 213 has reached the time periodTerr (Step S311: Y), the error determination unit 204 of the CPU 202determines that an error due to a failure of the main power switch 103has occurred (Step S312). In this case, the CPU 202 changes the firstpower supply ON signal 217 to the low level in order to deactivate thefirst power supply 207 (Step S313). In a case where the first powersupply ON signal 217 changes to the low level, the first power supply207 stops applying the DC voltage to the load 209. The errordetermination unit 204 of the CPU 202 transmits the display instructionsignal 215 indicating that the main power switch 103 has failed to thedisplay 101 (Step S314). Thus, the message which indicates that the mainpower switch 103 has failed is displayed on the display 101, forexample. This is processing performed in a case where the main powerswitch 103 has failed. In a case where the main power switch 103 hasfailed, the switch depression signal 212 is continuously in the state ofhigh level for the time period Terr or more.

(Processing Upon Shutdown)

FIG. 4A to FIG. 4C are flow charts for illustrating processing uponshutdown of the image forming apparatus 100.

The CPU 202 determines whether the main power switch 103 has beendepressed, and then the switch depression signal 212 has changed fromthe low level to the high level (Step S401). In a case where the switchdepression signal 212 has changed from low to high (Step S401: Y), theCPU 202 performs deactivation determination processing for the firstpower supply 207 (Step S402). In the deactivation determinationprocessing for the first power supply 207, it is determined whether themain power switch 103 has been depressed for the predetermined timeperiod (time period Ton/off) or more. With this processing, it ispossible to prevent such an erroneous operation as in a case where theuser has erroneously depressed the main power switch 103, for example.

In FIG. 4B, the deactivation determination processing for the firstpower supply 207 in Step S402 is illustrated. The CPU 202 startscounting the time period during which the switch depression signal 212,which is acquired from the main power switch 103, is at the high levelby the depression time period counter 203 (Step S405). The errordetermination unit 204 determines whether the counted time period 213obtained by the depression time period counter 203 has reached the timeperiod Ton/off (Step S406).

In a case where the counted time period 213 has not reached the timeperiod Ton/off (Step S406: N), the CPU 202 determines whether the switchdepression signal 212 has changed to the low level (Step S407). In acase where the switch depression signal 212 remains at the high level(Step S407: N), the CPU 202 compares the counted time period 213 and thetime period Ton/off again by the error determination unit 204.

The switch depression signal 212 having changed to the low level (StepS407: Y) means that the depressed state of the main power switch 103 hasbeen canceled before the shutdown processing is started. In this case,the CPU 202 clears the counted time period 213 of the depression timeperiod counter 203 to 0, and ends counting the time period by thedepression time period counter 203 (Step S408 and Step S409). The CPU202 returns to the processing of Step S401 without performing theshutdown processing. This is processing performed in the case of anerroneous operation by the user.

In a case where the counted time period 213 has reached the time periodTon/off (Step S406: Y), the CPU 202 ends the deactivation determinationprocessing for the first power supply 207. This is processing performedin a case of an instruction for shutdown intended by the user.

In a case where the main power switch 103 is continuously depressed forthe predetermined time period or more, and then the deactivationdetermination processing for the first power supply 207 is ended, theCPU 202 deactivates the first power supply 207 (Step S403). The CPU 202changes the first power supply ON signal 217 to the low level by thepower supply controller 205. In a case where the first power supply ONsignal 217 changes to the low level, the first power supply 207 isdeactivated to end applying the DC voltage to the load 209.

Next, the CPU 202 performs failure determination processing for the mainpower switch 103 (Step S404). In FIG. 4C, the failure determinationprocessing for the main power switch 103 in Step S404 is illustrated.

The CPU 202 determines whether the counted time period 213 correspondingto the time period during which the switch depression signal 212 is atthe high level, has reached the time period Ten (Step S411). In a casewhere the counted time period 213 is less than the time period Terr(Step S411: N), the CPU 202 determines whether the switch depressionsignal 212 has changed to the low level (Step S415). In a case where theswitch depression signal 212 remains at the high level (Step S415: N),the CPU 202 compares the counted time period 213 and the time periodTerr again by the error determination unit 204.

The switch depression signal 212 having changed to the low level (StepS415: Y) means that the depressed state of the main power switch 103 hasbeen canceled after the shutdown processing. In this case, the CPU 202clears the counted time period 213 of the depression time period counter203 to 0, and ends counting the time period by the depression timeperiod counter 203 (Step S416 and Step S417). The CPU 202 changes thepower transistor ON signal 216 to the low level to cut off (turn off)the power transistor 211. In a case where the power transistor 211 iscut off, the application of the DC voltage from the second power supply208 to the display 101 is ended. Therefore, the display 101 isdeactivated (Step S414). This is processing performed in the case wherethe main power switch 103 operates normally. In the case where the mainpower switch 103 operates normally, the switch depression signal 212changes to the low level after the state of high level has continued forthe time period Ton/off or more and for less than the time period Terr.

In a case where the counted time period 213 has reached the time periodTerr (Step S411: Y), the error determination unit 204 of the CPU 202determines that an error due to a failure of the main power switch 103has occurred (Step S412). In this case, the CPU 202 transmits thedisplay instruction signal 215 indicating that the main power switch 103has failed to the display 101 (Step S413). Thus, the message whichindicates that the main power switch 103 has failed is displayed on thedisplay 101, for example. This is processing performed in a case wherethe main power switch 103 has failed. In a case where the main powerswitch 103 has failed, the switch depression signal 212 is continuouslyin the state of high level for the time period Terr or more.

(Timing Charts Upon Startup)

FIG. 5A and FIG. 5B are timing charts obtained upon the image formingapparatus 100 is started. In FIG. 5A and FIG. 5B, timings of the switchdepression signal 212, the DC voltage output from the first power supply207, and the DC voltage applied to the display 101 are illustrated. FIG.5A is a timing chart obtained in the case of normal operation. FIG. 5Bis a timing chart obtained in a case where the main power switch 103 hasfailed.

In the case where the main power switch 103 operates normally, in a casewhere the main power switch 103 is depressed, the switch depressionsignal 212 changes from the low level to the high level. At a timing atwhich a period of high level has continued for the time period Ton/off,the first power supply 207 is activated, and the DC voltage is appliedto the display 101. In a case where the switch depression signal 212changes from the high level to the low level with the period of highlevel being less than the time period Terr, each of the first powersupply 207 and the display 101 enters an active state.

In the case where the main power switch 103 has failed, the timings fromwhen the first power supply 207 is activated to when the DC voltage isapplied to the display 101 are the same as in the case in which the mainpower switch 103 normally operates. In a case where the switchdepression signal 212 remains at the high level after the time periodTerr has elapsed, the CPU 202 determines that the main power switch 103has failed, and forcefully deactivates the first power supply 207. Thedisplay 101 remains in the active state with the DC voltage beingapplied thereto because it is required for the display 101 to displaythe message.

(Timing Charts Upon Shutdown)

FIG. 6A and FIG. 6B are timing charts obtained upon the image formingapparatus 100 is shut down. In FIG. 6A and FIG. 6B, timings of theswitch depression signal 212, the DC voltage output from the first powersupply 207, and the DC voltage applied to the display 101 areillustrated. FIG. 6A is a timing chart obtained in the case of normaloperation. FIG. 6B is a timing chart obtained in a case where the mainpower switch 103 has failed.

In the case where the main power switch 103 operates normally, in a casewhere the main power switch 103 is depressed, the switch depressionsignal 212 changes from the low level to the high level. At a timing atwhich a period of high level has continued for the time period Ton/off,the first power supply 207 is deactivated. In a case where the switchdepression signal 212 changes from the high level to the low level, andthe period of high level is less than the time period Terr, theapplication of the DC voltage to the display 101 is ended. The display101 is deactivated at the time in a case where there is no fear that themain power switch 103 fails.

In the case where the main power switch 103 has failed, the timings toin a case where the first power supply 207 is deactivated are the sameas in the case in which the main power switch 103 normally operates. Ina case where the switch depression signal 212 remains at the high levelafter the time period Terr has elapsed, the CPU 202 determines that themain power switch 103 has failed. The display 101 remains in the activestate with the DC voltage being applied thereto because it is requiredfor the display 101 to display the message.

The power supply control device of the image forming apparatus 100according to this embodiment described above determines that the mainpower switch 103 has failed in a case where the main power switch 103,which outputs the switch depression signal 212 in one state when it isnot depressed, has been depressed and the switch depression signal 212remains the one state for the predetermined time period. In this case,the power supply control device forcefully stops applying the DC voltageto the load 209, to thereby prevent the situation in which the operationof the load 209 cannot be stopped due to the failure of the main powerswitch 103. Further, the power supply control device displays themessage which indicates that the main power switch 103 has failed on thedisplay 101. Therefore, the user can determine what part of theapparatus has failed. As described above, according to this embodiment,even when the main power switch 103 has failed, the failure can bedetected and the apparatus can be shut down.

In this embodiment, there is adopted the configuration in which theapplication state of the DC voltage to the load 209 is switched in acase where the switch depression signal 212 has changed from the lowlevel to the high level and is continuously at the high level for thepredetermined time period (time period Ton/off) or more. Alternatively,the timing at which the application state of the DC voltage to the load209 is switched may be a timing at which the switch depression signal212 changes from the high level to the low level, for example.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2019-073025, filed Apr. 5, 2019, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A power supply control device comprising: aswitch configured to output a switch depression signal, which is in afirst logic level during a period in which the switch is not depressed,and is in a second logic level during a period in which the switch isdepressed; a first power supply configured to generate a first DCvoltage based on AC power, which is supplied from an outside, and toapply the first DC voltage to a predetermined load; a second powersupply configured to generate a second DC voltage based on the AC powerirrespective of a state of the switch; and a controller configured tooperate on the second DC voltage, to switch an operation state of thefirst power supply in a case where the switch depression signal hasswitched from the first logic level to the second logic level andthereafter the switch depression signal remains at the second logiclevel until a first predetermined time period has elapsed, and to outputa signal on a failure of the switch in a case where the switchdepression signal has switched from the first logic level to the secondlogic level and thereafter the switch depression signal remains at thesecond logic level until a second predetermined time period has elapsed,the second predetermined time period being longer than the firstpredetermined time period.
 2. The power supply control device accordingto claim 1, further comprising a display, wherein the controller isconfigured to output, as the signal on the failure of the switch, asignal for causing the display to display a message which indicates thatthe switch has failed.
 3. The power supply control device according toclaim 2, further comprising an energization controller provided on asupply path, through which the second DC voltage is applied from thesecond power supply to the display, to control energization of thedisplay with the second DC voltage, wherein the controller is configuredto control conduction of the energization controller depending on a timeperiod during which the second logic level continues from when theswitch depression signal has switched from the first logic level to thesecond logic level, to thereby control an operation state of thedisplay.
 4. The power supply control device according to claim 3,wherein the controller is configured to activate the first power supplyand conduct the energization controller to activate the display in acase where, under an inactive state of the first power supply, theswitch depression signal has switched from the first logic level to thesecond logic level and thereafter the switch depression signal remainsat the second logic level until the first predetermined time period haselapsed, and to cause the display to display the message which indicatesthat the switch has failed and deactivate the first power supply in acase where the switch depression signal has switched from the firstlogic level to the second logic level and thereafter the switchdepression signal remains at the second logic level until the secondpredetermined time period has elapsed.
 5. The power supply controldevice according to claim 4, wherein the controller is configured toactivate the first power supply and the display in a case where theswitch depression signal has switched from the first logic level to thesecond logic level and thereafter the switch depression signal switchesto the first logic level before the second predetermined time period haselapsed.
 6. The power supply control device according to claim 3,wherein the controller is configured to deactivate the first powersupply in a case where, under an active state of the first power supply,the switch depression signal has switched from the first logic level tothe second logic level and thereafter the switch depression signalremains at the second logic level until the first predetermined timeperiod has elapsed, and to cause the display to display the messagewhich indicates that the switch has failed in a case where the switchdepression signal has switched from the first logic level to the secondlogic level and thereafter the switch depression signal remains at thesecond logic level until the second predetermined time period haselapsed.
 7. The power supply control device according to claim 6,wherein the controller is configured to cut off the energizationcontroller to deactivate the display in a case where the switchdepression signal has switched from the first logic level to the secondlogic level and thereafter the switch depression signal switches to thefirst logic level before the second predetermined time period haselapsed.
 8. The power supply control device according to claim 1,wherein the controller is configured to: count a time period duringwhich the switch depression signal is continuously at the second logiclevel; and switch the operation state of the first power supply in acase where the counted time period reaches the first predetermined timeperiod, and deactivate the first power supply in a case where thecounted time period then reaches the second predetermined time period.9. The power supply control device according to claim 8, wherein thecontroller is configured to clear the counted time period to 0 and endthe counting in a case where the switch depression signal switches fromthe second logic level to the first logic level before the counted timeperiod reaches the second predetermined time period.
 10. The powersupply control device according to claim 8, wherein the controller isconfigured to clear the counted time period to 0 and end the counting ina case where the switch depression signal switches from the second logiclevel to the first logic level before the counted time period reachesthe first predetermined time period.
 11. An image forming apparatuscomprising: a load to be used in forming an image; a switch configuredto output a switch depression signal, which is in a first logic levelduring a period in which the switch is not depressed, and is in a secondlogic level during a period in which the switch is depressed; a firstpower supply configured to generate a first DC voltage based on ACpower, which is supplied from an outside, and apply the first DC voltageto the load; a second power supply configured to generate a second DCvoltage based on the AC power irrespective of a state of the switch; anda controller configured to operate on the second DC voltage, to switchan operation state of the first power supply in a case where the switchdepression signal has switched from the first logic level to the secondlogic level and thereafter the switch depression signal remains at thesecond logic level until a first predetermined time period has elapsed,and to output a signal on a failure of the switch in a case where theswitch depression signal has switched from the first logic level to thesecond logic level and thereafter the switch depression signal remainsat the second logic level until a second predetermined time period haselapsed, the second predetermined time period being longer than thefirst predetermined time period.